Flash memory is a non-volatile type of erasable and rewritable memory, which has experienced a good deal of success due to its relatively inexpensive nature. In many instances, flash memory is erased and programmed in large blocks. Implementations of flash memory have included external memory such as memory cards and flash drives, as well as internal memory, such as solid state storage for hand-held or mobile devices.
Flash memory devices are operated in a variety of manners. In many applications, a command mode is used for operations such as erasing and programming, and a memory mode is used for reading data from the flash. In some applications, flash devices use a half-duplex command-driven serial peripheral interface (SPI) protocol for device setup/initialization, and then move to a half-duplex command-driven 4-bit protocol for normal operation. However, different flash devices accept and/or require different commands and command formats. In many cases, flash devices are not compatible with certain types of other devices or processors. In addition, many forms of flash memory are not amenable to rapid access as required or desirable in certain applications.
These and other issues continue to present challenges to the utilization of serial flash memory.